Molecular weight controller for polymerization of lactams to polyamides

ABSTRACT

A molecular weight controller having particular application in the polymerization of a lactam, i.e., epsiloncaprolactam, to a polyamide, i.e., poly(epsiloncaprolactam). The molecular weight controller comprises a primary monofunctional amine, i.e., benzylamine, a primary monofunctional acid, i.e., acetic acid, and a salified aminoacid containing an aromatic, a cyclohexane, or cyclopentane moiety, i.e., 4-(aminomethylbenzoic acid salified with p-toluenesulfonic acid. The resulting polyamide has a reduced water extractable content.

This is a continuation of co-pending application Ser. No. 07/156,396filed on Feb. 16, 1988.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to molecular weight controllers useful in thepolymerization of lactams to polyamides, which find particularapplication in the melt-spinning of filamentary structures.

2. Description of the Prior Art

Fibers comprised of polyamides, especially poly(epsiloncaprolactam),otherwise known as nylon 6, find widespread commercial use in view oftheir highly desirable physical, chemical, and aesthetic qualities.

The term "fiber" as used herein includes fibers of extreme or indefinitelength (i.e., filaments) and fibers of short length (i.e., staple). Theterm "yarn" as used herein means a continuous strand of fibers.

Fibers of polyamides, including those of nylon 6, are usually preparedby the melt extrusion of molten polyamide through spinnerette platescontaining small-dimensioned orifices. A common procedure for producingthe polyamides and, in particular, nylon 6, involves the polymerizationof epsiloncaprolactam at sufficient temperatures and in the presence ofwater which serves to initiate the polymerization. Polymers prepared inthis manner, however, usually contain more than 10 percent waterextractable material which usually comprises caprolactam monomers andlinear and cyclic oligomers. The oligomers are mainly low molecularweight cyclic condensation products of epsiloncaprolactam. The presenceof such water extractable material has an adverse effect on theperformance of the polymer in the extrusion shaping of fibers and evenlarger-dimensioned articles such as pipes. To produce fibers havingsatisfactory physical properties, the water extractable content, whichconsists of oligomers and monomers (epsilon-caprolactam), should be lessthan 2.5 percent by weight of the polymer. The monomer content should beless than 0.5 percent by weight of the polymer.

Various procedures have been utilized to remove water extractablematerials from polyamides prior to their melt spinning. The most commonapproach involves the hot water leaching of the nylon 6 in granular formto remove water extractable material, followed by thorough drying priorto its melt extrusion. Another technique employed has been to subjectmolten nylon 6, generally in the form of thin films or shallow layers,to an extremely high vacuum, which removes the relatively volatileepsiloncaprolactam monomer but has only a minor effect on the lessvolatile oligomer materials. Such purification techniques involveadditional processing steps with an attendant increased manufacturingcost. In addition, regardless of the purification technique applied tothe nylon 6, once the reaction mass is no longer under the influence ofvacuum, the monomer can reform at high temperature within the polymerprior to spinning.

In order to reduce the extra manufacturing costs involving purifyingpolyamides, i.e., poly(epsiloncaprolactam), various procedures have beenproposed for the continuous production of caprolactam having a reducedamount of water extractable material. Such procedures include, forexample, the addition to the polymerization reaction of an organic acidmaterial, or an organic basic material or combinations thereof asmolecular weight controllers or chain terminators.

As described in U.S. Pat. No. 4,574,054, which is hereby incorporated byreference, in order to lower the formation rate of water extractablematerials, it is necessary to synthesize polyamides having a low contentof terminal amino groups. However, polymerization kinetics require acertain amount of terminal groups (both amino and carboxylic) andterminal amino groups are necessary in order to provide the polyamideswith an affinity for anionic dyestuffs.

The present invention provides a molecular weight controller forpolymerizing lactams to polyamides which overcomes or at least mitigatesthe above-described problems.

SUMMARY OF THE INVENTION

The surprising discovery has now been made that a polyamide having a lowcontent of water extractables and an affinity for anionic dyestuffs canbe prepared using a molecular weight controller comprising amonofunctional primary amine, a monofunctional organic acid, and anaminoacid containing a cyclic structure of 5 or 6 carbon atoms andhaving its amino groups salified by an acid.

The polyamides and, in particular, nylon 6, prepared utilizing themolecular weight controllers of the present invention have a terminalamino-group content in the range of from about 22 to 42 equiv/10⁶ g anda terminal carboxylic group content in the range of from about 10 to 15equiv/10⁶ g. Generally, the water extractable content is less than 0.7%by weight of polyamide, including a monomer content of less than 0.25%and an oligomer content of less than 2.0%. Thus, a commercial polyamideis produced having excellent affinity with anionic dyestuffs. Thepolyamides find particular use as yarns in textile applications.

The precise manner in which the molecular weight controllers function toproduce the polyamide having the desired properties is not fullyunderstood and need not be. Although the invention is not intended to belimited to any particular theory of operation, it is believed that thecyclic structure contained in the salified aminoacid, due to itsrigidity, is especially effective in preventing the formation ofundesirable cyclic oligomers in addition to preventing the formation oflinear oligomers and monomers. Regardless of the theory proposed, it issufficient to point out that the molecular weight controllers operatesuccessfully in the manner disclosed herein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The molecular weight controllers of the present invention comprise thefollowing ingredients:

(1) a monofunctional primary amine having a boiling point of at least180° C. at atmospheric pressure and a basic dissociation constant of atleast 1.7×10⁻⁵ ;

(2) a monofunctional organic acid having an acid dissociation constantof at least 1.5×10⁻⁵ ; and,

(3) an aminoacid containing a cyclic structure of 5 or 6 carbon atoms,having a total number of carbon atoms in the range of from about 6 toabout 9 carbon atoms, and having its amino group salified by amono-functional acid having an acid dissociation constant of at least1.0×10⁻².

Examples of preferred monofunctional primary amines include primaryaliphatic amines such as nonylamine, decylamine, and dodecylamine, andprimary aromatic amines and derivatives of said amines which aresubstituted in the ring, such as benzylamine, α-phenylethylamine, andβ-phenylethylamine, and mixtures thereof.

Examples of preferred monofunctional organic acids includemonofunctional carboxylic acids containing at least 2 carbon atoms, suchas acetic acid, propionic acid, n-butyric acid, isobutyric acid,n-valeric acid, trimethylacetic acid, caproic acid, and pelargonic acid,and monofunctional aromatic acids such as benzoic acid and napthionicacid, and mixtures thereof.

Examples of aminoacids corresponding to ingredient (3) includeaminoacids containing an aromatic, cyclohexane, or cyclopentane moiety.Examples of preferred aminoacids include aminocyclohexanecarboxylicacids such as compounds represented by the following formula: ##STR1##wherein:

X is H₂ N-- or NH₂ R¹ --, R¹ is methylene or ethylene, and X occupiesone of the two 3 positions or the 4 position with respect to thecarboxylic acid moiety.

Examples of compounds corresponding to formula I includetrans-1,4-aminocyclohexanecarboxylic acid,cis-1,4-aminocyclohexanecarboxylic acid,trans-1,3-aminocyclohexanecarboxylic acid,cis-1,3-aminocyclohexanecarboxylic acid,cis-1(aminomethyl)-3-cyclohexanecarboxylic acid,trans-1(aminomethyl)-3-cyclohexanecarboxylic acid,cis-1(aminoethyl)-3-cyclohexanecarboxylic acid,trans-1(aminoethyl-3-cyclohexanecarboxylic acid,cis-1(aminomethyl)-4-cyclohexanecarboxylic acid,trans-1-(aminomethyl)-4-cyclohexanecarboxylic acid,cis-1(aminoethyl)-4-cyclohexanecarboxylic acid,trans-1-(aminoethyl)-4-cyclohexanecarboxylic acid, and mixtures thereof.

Another example of preferred aminoacids comprises aminobenzoic acidsrepresented by the following formula: ##STR2## wherein:

Y is H₂ N-- or NH₂ R² --, R² is methylene or ethylene, and Y occupiesthe para position or one of the two meta positions with respect to thecarboxylic acid moiety.

Examples of compounds corresponding to formula II include p-aminobenzoicacid, m-aminobenzoic acid, 4(aminomethyl) benzoic acid,4-(aminoethyl)benzoic acid, 3-(aminomethyl)benzoic acid,3-(aminoethyl)benzoic acid, and mixtures thereof.

An example of another class of aminoacid suitable for use in theinvention are aminocyclopentane carboxylic acids represented by thefollowing formula: ##STR3## wherein:

Q is H₂ N-- or H₂ NR³ --, and R³ is methylene, ethylene, propylene orisopropylene.

Examples of compounds which correspond to formula III include3-aminocyclopentanecarboxylic acid, 3-(aminomethyl) cyclopentanecarboxylic acid, 3-(aminoethyl)cyclopentanecarboxylic acid,3-(aminopencyl)cyclopentanecarboxylic acid,3-(aminoisopropyl)cyclopentanecarboxylic acid,3-(aminoisopropyl)cyclopentanecarboxylic acid, and mixtures thereof.

Examples of preferred salifying acids include aromatic sulfonic acidssuch as p-toluenesulfonic acid, naphthalenesulfonic acid,benzenesulfonic acid, 4-methylbenzenesulfonic acid, cycloalkylsulfonicacids such as cyclohexanesulfonic acid, and inorganic acids includinghydrohalogen acids such as hydrobromic acid and hydrochloric acid,phosphoric acids such as metaphosphoric acid, and orthophosphoric acid,sulfuric acid, and mixtures thereof.

The molecular weight controllers of the present invention areparticularly effective with polyamides containing some free reactivecarboxylic acid groups. The term polyamide is intended to include allthe linear chain polymers containing characteristic amide (-NHCO)groups. The preferred class of polyamides suitable for use in thepresent invention is represented by the following formula: ##STR4##wherein:

s is a positive integer and has a value from 3 to 11 and t is a positiveinteger and represents the number of monomer units in the polymerrequired to achieve the desired molecular weight.

Examples of commercially important polyamides of this class includenylon 4, nylon 11, nylon 12, and, particularly, nylon 6 (s equals 5).

The preferred molecular weight of the polyamides produced using themolecular weight controllers of the present invention will generally bea number average molecular weight in the range of from about 10,000 toabout 25,000 and, more preferably, will be a number average molecularweight of from about 16,000 to about 20,000.

Generally, the amount of molecular weight controller utilized forpolymerization of the lactam will be an amount in the range of fromabout 30 equiv/10⁶ g to about 100 equiv/10⁶ g based on the weight of thepolymer. More preferably, the amount will be an amount in the range offrom about 35 to about 60 equiv/10⁶ g based on the weight of thepolymer.

The amount of monofunctional primary amine, monofunctional organic acid,and salified amino acid present in the molecular weight controller willvary over a wide range with no limitation. As a general rule, however,the molecular weight controller will comprise an aqueous compositioncontaining from about 40.0 to about 60.0 mole percent monofunctionalprimary amine, about 15.0 to about 30.0 mole percent of monofunctionalorganic acid, and 20.0 to about 40.0 mole percent salified aminoacidbased on the total moles of the three ingredients. More preferably, theaqueous molecular weight controller will contain about 48.0 to about52.0 mole percent primary amine, about 18 to about 22 mole percentmonofunctional organic acid, and about 28.0 to about 32.0 mole percentsalified aminoacid based on the total moles of the three ingredients.

Procedures of polymerizing the lactam to form the polyamide are known topersons skilled in the art. Preferably, the polymerization reaction iscarried out at a temperature in the range of from about 220° to about280° C. The hydrolysis and polyaddition portion of the reaction iscarried out at atmospheric pressure or, in other words, the normalpressure of the vessel used for this portion of the reaction and thepolycondensation portion of the reaction is preferably carried out undera strong vacuum, 5mm of mercury or less. The time for the polymerizationis generally 5 to about 20 hours.

Thereafter, the polyamide can be vacuum extracted and then extruded toform one or more fibers. The extruded fibers are then cooled andthereafter processed (drawn, crimped, etc.) in accordance with the finalapplication of the fibers.

Although the molecular weight controller finds particular application ina continuous process, they can also be utilized in discontinuouspolymerization procedures.

In addition to molecular weight controllers, other property-modifyingingredients can be incorporated into the polyamides in any desiredamount. Examples of such additives include fire-retarding agents such asantimony, phosphorus, and halogen compounds; delustrants such astitanium dioxide; antistatic agents; heat and light stabilizers such asinorganic reducing ions; transition metal ions such as Mn⁺², Cu⁺², Sn⁺²; phosphites, organic amines such as alkylated aromatic amines andketone aromatic amine condensates; thermally stable pigments;fluorescing agents and brighteners; bacteriostats such as phenols andquaternary amines; antisoiling agents and the like. These additives canbe incorporated into the polymer at any stage of the reaction, whetheras concentrates distributed in the monomer or in preformed polyamide.For operational efficiency, however, the additives are preferablyintroduced together with the molecular weight controllers at thecommencement of the process. Proper dispersion of these ingredientswithin the polymer is achieved by means conventional in the art.

The invention is further exemplified by the example below which ispresented to illustrate certain specific embodiments of the invention,but is not intended to be construed so as to be restrictive of the scopeand spirit thereof.

EXAMPLE

Tables I and II set forth the abbreviations used in the Example.

                  TABLE I                                                         ______________________________________                                        Abbreviation   Chemical                                                       ______________________________________                                        CL             caprolactam                                                    BAM            benzylamine                                                    HAC            acetic acid                                                    A/S            4-(aminomethyl)benzoic acid                                                   salified with  -p-toluenesulfonic                                             acid                                                           ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Abbreviation   Measurement                                                    ______________________________________                                        RV             relative viscosity                                             CD             cyclic dimer                                                   AEC            terminal amino-group content                                   COOH           terminal carboxylic group                                                     content                                                        MWC            molecular weight controller                                    CL             caprolactam monomer                                            ______________________________________                                    

Relative viscosity, which is a measure for the molecular weight of thepolymer, was determined using standard procedures wherein theconcentration of the measuring solution is 10 g/liter, the solvent is 96percent by weight sulfuric acid, and the measuring temperature is 25° C.

Throughout the Example, all percentages are by weight, unless otherwisespecified.

The terminal amino-group content and terminal carboxylic content of thepoly(caprolactam) reported in the examples was determined using standardtitration procedures. The poly(caprolactam) was dissolved in hot benzylalcohol and the amine end groups were then titrated to the thymol blueend point with methanolic HCl. The carboxylic acid end points weretitrated to the Cresol red end point with methanolic NaOH.

The determination of amounts of caprolactam monomer and cyclic dimerreported in the Example was determined by gas chromatography.

A series of tests was carried out introducing 339 parts by weightcaprolactam and molecular weight controllers of the present inventioninto a sealed vessel. The mixtures were heated to 250° C. for a totalperiod of 24 hours. Atmospheric pressure was maintained on the vesselduring this time except during vacuum extraction. The vacuum extractionwas carried out at a pressure of less than 1 mm or mercury. Next, thepolycaprolactam was extruded and the impurities were extracted by meansof hot water. Measurements of the impurities of the poly(caprolactam)were measured at the end of both of these steps. After the hot waterextraction step, the polycaprolactam was dried to where it containedless than 500 ppm of water, introduced into a tube held under a staticnitrogen blanket and heated at 260° C. for periods of 30, 60, and 90minutes. After the heating, the polymer was removed from the tube andanalyzed. The results of these tests are reported in Table III.

                                      TABLE III                                   __________________________________________________________________________             EXTRUDED POLYMER        ANALYSIS OF EXTRUDED,                        TEST MWC ANALYSIS                WASHED, AND DRIED POLYMER                    NO.  (g) RV  AEC COOH CL (%)                                                                              CD (%)                                                                             RV  AEC COOH CL (%)                                                                              CD (%)                                                                              H.sub.2 O           __________________________________________________________________________                                                              (%)                 1    BAM 2.26                                                                              32  24   0.08  0.31 2.31                                                                              34  21   0.005 0.03  0.04                     (1.83)                                                                        HAC                                                                           (0.78)                                                                        H.sub.2 O                                                                     (3.60)                                                                        A/S                                                                           (0.97)                                                                   2    BAM 2.26                                                                              32  24   0.08  0.31 2.31                                                                              34  21   0.005 0.03  0.04                     (1.83)                                                                        HAC                                                                           (0.78)                                                                        H.sub.2 O                                                                     (3.60)                                                                        A/S                                                                           (0.97)                                                                   3    BAM 2.33                                                                              32  20   0.06  0.19 2.35                                                                              31  18   0.01  0.07  0.038                    (1.83)                                                                        HAC                                                                           (0.78)                                                                        H.sub.2 O                                                                     (3.60)                                                                        A/S                                                                           (0.97)                                                                   4    BAM 2.35                                                                              33  21   0.06  0.29 2.33                                                                              34  20   0.009  0.044                                                                              0.018                    (1.83)                                                                        HAC                                                                           (0.78)                                                                        H.sub.2 O                                                                     (3.67)                                                                        A/S                                                                           (0.95)                                                                   __________________________________________________________________________            ANALYSIS OF POLYMER HEATED AT 260° C.                                  30 MINUTES        60 MINUTES        90 MINUTES                        TEST                                                                              MWC                CD                CD                 CD                NO. (g) RV AEC                                                                              COOH                                                                              CL (%)                                                                             (%)                                                                              RV AEC                                                                              COOH                                                                              CL (%)                                                                             (%)                                                                              RV AEC COOH                                                                              CL                                                                                 (%)               __________________________________________________________________________    1   BAM 2.26                                                                             24 24  0.29 0.07                                                                             2.33                                                                             28 24  0.48 0.1                                                                              2.33                                                                             27  22  0.57 0.11                  (1.83)                                                                        HAC                                                                           (0.78)                                                                        H.sub.2 O                                                                     (3.60)                                                                        A/S                                                                           (0.97)                                                                    2   BAM 2.31                                                                             27 23  0.25 0.04                                                                             2.33                                                                             28 22  0.38 0.03                                                                             2.26                                                                             27  23  0.53 0.02                  (1.83)                                                                        HAC                                                                           (0.78)                                                                        H.sub.2 O                                                                     (3.60)                                                                        A/S                                                                           (0.97)                                                                    3   BAM 2.36                                                                             29 21  0.17 0.037                                                                            2.36                                                                             30 21  0.23 0.041                                                                            2.38                                                                             28  20  0.66 0.055                 (1.83)                                                                        HAC                                                                           (0.78)                                                                        H.sub.2 O                                                                     (3.60)                                                                        A/S                                                                           (0.97)                                                                    4   BAM 2.34                                                                             31 22  0.07 0.058                                                                            2.34                                                                             32 21  0.21 0.058                                                                            2.35                                                                             30  20  0.46 0.061                 (1.83)                                                                        HAC                                                                           (0.78)                                                                        H.sub.2 O                                                                     (3.67)                                                                        A/S                                                                           (0.95)                                                                    __________________________________________________________________________

The results of the tests demonstrate the effectiveness of the molecularweight controllers of the present invention in reducing monomer andcyclic dimer content of the resulting poly(epsiloncaprolactam). Evenafter heating the polycaprolactam at 260° C. for a period of 90 minutes,the reformation of monomers and cyclic dimer was very low.

Although certain preferred embodiments of the invention have beendescribed for illustrative purposes, it will be appreciated that variousmodifications and innovations of the procedures and compositions recitedherein may be effected without departure from the basic principles whichunderlie the invention. Changes of this type are therefore deemed to liewithin the spirit and scope of the invention except as may benecessarily limited by the amended claims or reasonable equivalentsthereof.

What is claimed is:
 1. A polyamide molecular weight controllercomprising:(a) a monofunctional primary amine having a boiling point ofat least 180° C. at atmospheric pressure and a basic dissociationconstant of at least 1.7×10⁻⁵ ; (b) a monofunctional organic acid havingan acid dissociation constant of at least 1.5×10⁻⁵ ; and (c) anaminoacid containing a cyclic structure of 5 or 6 carbon atoms, a totalnumber of carbon atoms in the range from about 6 to about 9, and havingits amino group salified by a monofunctional acid having an aciddissociation constant of at least 1.0×10⁻².
 2. The molecular weightcontroller recited in claim 1 wherein said aminoacid is selected fromthe group consisting of ##STR5## wherein: X is H₂ N-- or NH₂ R¹ --, R¹is methylene or ethylene, and X occupies one of the two 3 positions orthe 4 position with respect to the carboxylic acid moiety; ##STR6##wherein: Y is H₂ N-- or NH₂ R² --, R² is methylene or ethylene, and Yoccupies the para position or one of the two meta positions with respectto the carboxylic acid moiety; ##STR7## wherein: Q is H₂ N-- or H₂ NR³--, and R³ is methylene, ethylene, propylene or isopropylene; and,mixtures thereof.
 3. The molecular weight controller recited in claim 2wherein said salifying acid is selected from the group consisting ofp-toluenesulfonic acid, naphthalenesulfonic acid, benzenesulfonic acid,4-methylbenzenesulfonic acid, cyclohexanesulfonic acid, acetic acid,hydrochloric acid, metaphosphoric acid, orthophosphoric acid, sulfuricacid, and mixtures thereof.
 4. The molecular weight controller recitedin claim 3 wherein said monofunctional primary amine is selected fromthe group consisting of nonylamine, decylamine, dodecylamine,α-phenylethylamine, β-phenylethylamine, benzylamine, and mixturesthereof.
 5. The molecular weight controller recited in claim 4 whereinsaid monofunctional organic acid is selected from the group consistingof acetic acid, propionic acid, n-butyric acid, isoburyric acid,n-valieric acid, trimethylacetic acid, caproic acid, pelargonic acid,benzoic acid, napthionic acid, and mixtures thereof.
 6. The molecularweight controller recited in claim 5 wherein said amino acid is selectedfrom the group consisting of trans-1,4-aminocyclohexanecarboxylic acid,cis-1,4-aminocyclohexanecarboxylic acid,trans-1,3-aminocyclohexanecarboxylic acid,cis-1,3-aminocyclohexanecarboxylic acid,cis-1(aminomethyl)-3-cyclohexanecarboxylic acid,trans-1(aminomethyl)-3-cyclohexanecarboxylic acid,cis-1(aminoethyl)-3-cyclohexanecarboxylic acid,trans-1(aminoethyl-3-cyclohexanecarboxylic acid,cis-1(aminomethyl)-4-cyclohexanecarboxylic acid,trans-1(aminomethyl)-4-cyclohexanecarboxylic acid, p-aminobenzoic acid,m-aminobenzoic acid, 4-(aminomethylbenzoic acid, 4-(aminoethyl)benzoicacid, 3-(aminomethyl)benzoic acid, 3-(aminoethyl)benzoic acid, andmixtures thereof.
 7. The molecular weight controller recited in claim 6wherein said monofunctional primary amine is present in an amount in therange of from about 40.0 to about 60.0 mole percent based on the totalmoles of said molecular weight controller.
 8. The molecular weightcontroller recited in claim 7 wherein said monofunctional organic acidis present in an amount in the range of from about 15.0 to about 30.0mole percent based on the total moles of said molecular weightcontroller.
 9. The molecular weight controller recited in claim 8wherein said salified aminoacid is present in an amount in the range offrom about 20.0 to about 40.0 mole percent based on the total moles ofsaid molecular weight controller.
 10. The molecular weight controllerrecited in claim 9 wherein said monofunctional primary amine isbenzylamine, said monofunctional organic acid is acetic acid, and saidsalified aminoacid is 4-(aminomethyl)cyclohexanecarboxylic acid salifiedwith p-toluene sulfonic acid or 4-(aminomethyl)benzoic acid salifiedwith p-toluenesulfonic acid.